Titanium dioxide is a material having diverse fields of application such as paints, plastics, cosmetics, inks, paper, chemical fiber, and optical catalysts. TiO2 is currently being produced all over the world using a sulfate and chloride process.
The sulfate process was commercialized in 1916 by a Norwegian company called Titan; this process produces TiO2 through a hydrolysis process and a calcination process at a temperature of 800 to 1000° C., and produces TiO2 powder through a pulverization process.
The chloride process was more recently developed in 1956 by Du Pont, a U.S. company. The major production reaction is a process of reacting TiCl4 with oxygen at a temperature of about 1500° C., thereby producing TiO2. Relative to the sulfate process, the chloride process has advantages in that the amount of waste is reduced, continuous processing is possible, and high-quality rutile TiO2 is produced; and hence the chloride process accounts for approximately 60% of the worldwide TiO2 production.
However, since Impurities are mixed and fed in and the reaction temperature is high during the sulfate and chloride processes, the sulfate and chloride processes are disadvantageous for synthesizing high-purity TiO2 particles with the submicron or nano size. As a result, many studies about a method of synthesizing nano-sized TiO2 particles have now been conducted.
Kim et al. disclosed a low temperature synthesis process of nano-sized rutile and a mixture of rutile and anatase in U.S. Pat. No. 6,001,326. They obtained rutile and a mixture of rutile and anatase by diluting an aqueous titanyl chloride solution to a concentration of about 0.2 to 1.2 and heating the diluted aqueous titanyl chloride solution at a temperature in the range of 15 to 155° C.
Musick et al. suggested a method of modifying a chloride process and synthesizing nano-sized powder in U.S. Published Patent Application No. 2006/0251573 A1. They described a method of synthesizing nano-sized particles with a size of about 80 to 100 nm by reacting titanium tetrachloride at a temperature of above 800° C. and with a pressure of about 5 to 25 psig in the presence of water vapor.
Yang et al. disclosed a process of producing rutile TiO2 using TiCl4 in Korean Patent No. 10-0420275. They suggested a method of producing crystalline TiO2 by preparing Ti aqueous solution of 0.1M to 1.4M by adding 0.01 to 5M of mineral acid and distilled water to TiCl4 at a temperature of −10 to 10° C., heating the prepared Ti aqueous solution at a temperature of 15 to 200° C. for about 24 hours, adding an alkali aqueous solution to the heated Ti aqueous solution, and then adjusting a final pH of the solution to 6 to 8.
The limitations of the prior art are overcome by the present invention as described below.